Some arc torches, for example the manual plasma-arc cutting torch sold by the firm La Soudure Autogene Francaise under the trademark Nertajet Zip, are equipped with a cap of this type. The skirt, which conducts around the plasma ejection nozzle a stream of compressed cooling air, is composed of a thermoplastic material so that it is possible to give it a relatively complex shape by injection moulding and obtain a good strength.